1. Field of the Invention
The present invention relates to a brake control apparatus for a vehicle.
2. Description of the Related Art
Recently, there has been developed a brake control technique which is applied to a motor-driven vehicle using a motor as a power source or a so-called hybrid vehicle using a motor and an internal combustion engine as a power source and which performs regeneration-coordinative brake control using braking force on the basis of hydraulic pressure (hydraulic braking force) as well as regenerative braking force generated by the motor.
More specifically, a brake apparatus for a vehicle which performs the above-described regeneration-coordinative brake control is generally designed to adjust the hydraulic braking force and the regenerative braking force in accordance with a force with which a brake pedal is operated (brake pedal depressing force) such that the characteristic of total braking force (entire braking force acting on the vehicle), which is the sum of the hydraulic braking force and the regenerative braking force, with respect to the brake pedal depressing force coincides with a preset target characteristic.
With this control, the characteristic of the total braking force with the brake pedal depressing force coincides with the preset target characteristic, and therefore, a driver does not receive an unnatural sensation at braking. In addition, during a period in which the driver decelerates the vehicle through operation of the brake pedal, electrical energy which is generated by the motor in accordance with the regenerative braking force of the motor can be collected in a battery, whereby the energy efficiency of the entire apparatus can be increased, and fuel consumption of the vehicle can be reduced.
In addition, a brake apparatus for a vehicle (antilock control apparatus for an electric automobile) described in Japanese Patent Application Laid-Open (kokai) No. H6-171489 is designed to further perform a known antiskid control operation (hereinafter called “ABS control”) when a wheel tends to lock during a period in which the brake pedal is being operated (and accordingly, the above-mentioned regeneration-coordinative brake control is being executed), so as to further adjust the hydraulic braking force acting on the wheel (decrease the hydraulic braking force in accordance with a predetermined pattern) to thereby prevent the wheel from locking.
Here, there will be considered a case where ABS control is performed for a wheel which is receiving regenerative braking force during performance of the regeneration-coordinative brake control (hereinafter called a “wheel undergoing regenerative braking”). In this case, if the regenerative braking force exerted on a wheel which undergoes ABS control during performance of ABS control (hereinafter called a “wheel undergoing ABS control”) is large, in some cases, locking of the wheel undergoing ABS control cannot be properly suppressed through only adjustment of the hydraulic braking force by the ABS control.
In other words, if a regenerative braking force is acting on a wheel undergoing ABS control during performance of ABS control, the regenerative braking force may adversely influence the ABS control. In view of the above, the apparatus disclosed in the publication is designed to adjust regenerative braking force to zero when ABS control is started and performed.
However, when the regenerative braking force is adjusted to zero, the quantity of electrical energy generated by the motor also becomes zero. Accordingly, adjusting the regenerative braking force to zero means that no electrical energy is collected in the battery at all during performance of ABS control. Accordingly, from the viewpoint of improving energy efficiency, it is preferred that even during performance of ABS control, regenerative braking force is generated within a range in which the regenerative braking force does not adversely influence the ABS control.